How Much Indigo in the Vat?

As I learned to use organic indigo vats, I started with recipes from Michel Garcia: “one, two, three”. Michel talks about the vats in simple terms. It’s as easy as 1,2,3. This also represents the proportions of indigo, lime, and sugar that go into the vat:

  • 1 part indigo
  • 2 parts lime
  • 3 parts fructose sugar

It’s simple, right?

Not always.

I probably get more questions about making and maintaining an indigo vat than anything else. There are so many unknowns. It’s taken me a number of years to feel comfortable with those unknowns and to gain the confidence to solve problems with the vat.

I recently had several people ask me about the quantity of indigo in the vat. That’s an important question. Unless you know how much indigo, you can’t really determine how much sugar (or other reduction material) or how much lime.

I’ve watched Michel make vats with very small amounts of indigo and what I would consider very large amounts of indigo. What is the difference? Will you get a darker color from a vat with more indigo?

The answer is “yes” and “no”.

I made 3 small fructose vats with varying amounts of indigo

  • 2 grams indigo per liter of vat liquid volume
  • 5 grams indigo per liter of vat liquid volume
  • 8 grams indigo per liter of vat liquid volume

As you can see from the samples dyed the very next day, there was a great deal of difference in the colors produced from each vat. Even on day 3 there was significant difference. But one week later, the 3 shades of blue are much more similar. All of these samples represent only one 20-minute dip in the vat.

Dye tests done with a single long dip in the three different vats

Why would you use 8 grams of indigo per liter instead of 2 when you can get a similar color from both these options? There is more indigo in the vat, which means more can be dyed over a longer period of time before additional indigo must be added. If I were doing a short-term vat for a small amount of dyeing, 2 grams of indigo per liter would probably be plenty.

The questions to ask are:

  • What  quantity of textiles will  be dyed in the vat?
  • How many people will be using the vat?
  • How long do you want to keep the vat?
  • How quickly to you need to get strong color from the vat?

The coloration of the reduced liquid in the 3 vats is different, indicating varying amounts of indigo in reduction. But the textile is only able to absorb so much dye at a time. We always build up color with multiple, long dips in the vat.

Three indigo vats reduced with fructose: 8 grams, 5 grams, and 2 grams of indigo per liter

The other thing you can see through these glass jars is the amount of sediment at the bottom of the vat. The weakest vat has very little and it gets progressively deeper with the stronger vats. It’s important to keep our textile above this sediment when it’s dyeing.

I currently have a 30-liter vat that I have been using for over a year now. I’ve added indigo to it a couple of times, and of course plenty of reduction material and lime. The vat is still working well but over the months the sediment has gotten very deep, which has reduced my dyeing space so much that it’s time to make a new vat.

The “1,2,3.. ” proportions are guidelines and easy to measure if you’re using fructose. How many bananas or sweet potatoes do you need to reduce 10 grams of indigo? Take a good guess. Making small experimental vats in glass jars has taught me a great deal about how the vat works. We don’t always know but have to start somewhere.

Observe carefully. One must be patient with the indigo vat.

23 thoughts on “How Much Indigo in the Vat?

  1. Hi Catharine,

    As always your posts seem to reflect the stages I am up to with my own vats and observations!

    However, I have found that my sediment reduces when I am not actively dyeing all the time (although I stir it every so often to keep it healthy and check its pH etc.) I thought (perhaps erroneously) that in order to keep the reduction going the vat uses up this ‘storehouse’ of sediment ….now I am writing this perhaps it doesn’t make sense at all, but I have found over the last 18 months I have kept my vat going when I add more materials the sediment is thicker, but when not used it gets ‘thin’. Joy will probably debunk this theory ! Also, I have been using 10g/l indigo as that was the recipe we started with, and I guess I don’t mind that because as you said, you don’t have to replenish it so often especially in class situations when you can’t control what people are putting into the vat all the time.

    It is helpful when the small test vats are in transparent bottles, unlike my large vats, so that you can actually see the sediment, but I have never left one of those go for an extended period of time (months?) to watch whether sediement gets thinner or not, have you?

    Thank you so much again for your posts, I make a point of passing them on to others.



    Julie Ryder 0414738251


    1. Interesting! I wish I had an answer to this, Julie, but it’s something else to observe and learn from. I will try and keep those small vats around for a time, dye with them, and see what happens. I will also check with Joy. She mentioned once that lime in particular causes a lot of sediment and I think it may be plaster (though I have not confirmed that). I also have a vat made with fructose and lye (sodium hydroxide) going and trying to make sense of that. We will all learn this together….. Thanks!

      1. and now I am wondering whether the sediment would be useful for something else, it always bothered me that I would lose the indigo in the sediment, so now I want to try and make tadelakt (waterproof lime plaster) with it. always for things to try

  2. Thank you Catherine for another fascinating article. I so look forward to receiving them and following your experiments and results. I keep them all for reference and I must say their scientific rigour is wonderful so repetition is possible…otherwise it’s just so hit and miss. Certainly it makes me so awe inspired at the thousands of years of knowledge that dyers in every culture are part of. Thank you.

    1. Hi Catharine!
      Really enjoyed this post. Seeing the vat in a clear container really brought some new insights for me. I understand why you would put the larger quantity of indigo in the vat (longer use, more dye capacity before having to add additional indigo) — but I’m not sure why the color of the 2 gm vat intensified over the period of a week. I could understand the colors of all three vats being similar at first and then the 2 gm vat diminishing first, the 5 gm diminishing next, and the 8 gm lasting longest — but I am puzzling over the 2 gm appearing to yield darker color over a week’s time.

      1. Elizabeth,
        I think that only a certain amount/proportion of the indigo goes into reduction in the first day or two. In the case of the the 2 g.vat there was only a small amount. The leuco color for all of the vats was lighter in color the first couple days.The other variable is that the textile can only absorb a certain amount of indigo. So even if the 8 gram vat has more indigo in reduction after a week, the cotton can only absorb so much. That’s my best guess!

  3. Hello Catherine, thanks for all your interesting posts. What happens when the fabric touch the sediment? You get spots? I have another question about the length of the dips. Do you dip the dirst time long and then shorter ones?

    1. Yes, you get spots, or areas that are not dyed well. The indigo is not in reduction in that sediment.
      I always use long dips. Otherwise the dye only gets to the surface of the textile and doesn’t have a chance to penetrate the fiber. It makes a big difference in the lightfastness of the dye.

      1. Hello! Thank you so much for sharing such a great information! I’ve read that the organic vat requires a long dip of 10-15min on your different post. Do you place a strainer or some sort at the bottom of your vat so that the fabric does not touch the sediment?

      2. Yes, I do. It might be a basket or other type of strainer. Sometimes I suspend the textiles from the top so that they do not touch the bottom of the vat.

      3. Thank you so much for taking time to reply and I’m so glad I came across your blog! I really appreciate you share your insights and all the amazing information!

  4. I know that this post refers to the amount of indigo dye – but could you address the temperature needed to keep the vat active? I am familiar with dyeing with indigo using lye and some heat, but I would like to move to a fermentation vat.


    1. I start my vat with hot water, close to 140-180°F. The hot water helps to speed up the initial reduction. Once the vat is in reduction the heat is not as critical. It cools down to room temperature and I don’t apply any heat after that. I think it would start OK with cooler water but it would be slower to go into reduction.

      I keep my vat in an unheated, concrete floor studio. Winter temperatures in the building can get into the low 40°s F. During the cold months I keep an aquarium heater in the vat. That seems to maintain the temperature at about 63° F and the vat is happy.

      1. Thank you. I’ve been afraid to try a vat due to the temperature. I will give it a try and investigate the aquarium heating concept, if needed.

  5. Perfect timing. I have an 8 gallon fructose vat going at home that I’ve had to revive from time to time. Your experiment helped so much. Hate to waste indigo.

    Reviving it has been difficult up to now. I keep the vat warm with fishtank heaters, but it can sit unused for two weeks or longer. I re-read your earlier posts on reviving. Reviving it seems to take as much fructose and lime as when I first made it. I had been just trying a cup of fructose here and there with little luck. Has that been the case with your revival efforts? More fructose.

    And one last question: I’ve got my 25b bag of fructose in a plastic bin. It still gets hard from moisture. Any tips on keeping fructose lose? Thanks, Peggy Cox

  6. Catharine, thank you! It was new to me that from a weak vat you can get still a strong color in longer time. I have gotten only pale color from fructose vats from my own grown woad or japanese indigo, but sadly I haven’t saved the vats for a longer time, which I obviously should have done. You must be right in that only a certain amount/proportion of the indigo goes to reduction, and longer time helps. Thanks to you now I will try them again!
    Another interesting thing will be if you can use lye (possibly woodash lye) with fructose vat, I am going to try it when the weather gets warmer. If it was possible that would be a good thing for many hobby dyers here in Finland, because lime can only be bought here in 25 kg bags, not in small amounts.

    1. I would be very interested in anything you learn about using wood ash lye with the organic reduction vat. I have tried this myself, thinking that the wood ash lye would eliminate some of the precipitate at the bottom of vat that comes from the lime. I made my own lye, which was plenty alkaline. But it did not work. My theory was that it was not “strong” enough, even though the alkalinity was OK. Maybe I wan’t patient enough with this! I’ve since done some experiments with sodium hydroxide and that worked, though the vat does look very different.

  7. Thank you for all the informative posts!

    Should the formula perhaps take the volume of the final vat into account? It would be very interesting to see whether the smaller amounts of indigo reduce as quickly as the 8 g/l vat if the same amount of water to lime and fructose were added to all three vats.

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